Amid all the things he hoarded - the carrier bags, the books, the magazines, the cat food, the bottles - the one thing that hasn't come to light is a photograph. It makes a kind of sense. After all, Gordon Stewart died buried in the detritus of his own life, his identity obliterated by his junk.

Stewart led a quiet, unremarkable life. He had not been in trouble with the police, he had made no outstanding contribution to the local community, he had no relatives and, at the time he died in January, he seemed to have no friends. Perhaps the one remarkable thing about his life was the manner of his death - it became national news. The headlines were cold and disturbing: "Man found dead in tunnel of rubbish at home", "Human mole Gordon Stewart dies of thirst", "Loner who built tunnels out of rubbish dies". The reports told us he was 74 years old, he wore a ponytail, he cycled everywhere, his neighbours did not know him well, though he had lived most of his life in this house in Aylesbury, and it had taken Thames Valley police many hours to discover him, then dig him out of the rubbish.

How could he have allowed himself and his house to get into this state? Why didn't neighbours do anything to help? Where were social services when they were needed? The death of Gordon Stewart raised many uncomfortable questions. It also touched many people who had never known him. Condolences appeared on a memorial website: "I hope that you have now found peace. It's just a shame you had such a lonely life," read one.

Aylesbury, part of the London commuter belt, is a quiet former market town in Buckinghamshire. The private estate where Stewart lived is just that - private. There is a Neighbourhood Watch badge on many doors, but this is a place where people keep to themselves and respect each other's privacy. The houses are semi-detached, with small but lovingly tended gardens. Stewart's house stands out. A week after his death was reported, windows, front door and garage are boarded up. The house is a two-up, two-down called Sandown. In the garage, a 50s car was found - it looked as if it hadn't been touched since then. The downstairs windowsill, visible below the boarding, is stacked with an extraordinary array of rubbish - cat litter, shredded newspapers, wallpaper, sandwich boxes. It's more a landfill than a living room.

Two environmental health officers from Aylesbury Vale council have accompanied me to the house. Richard Swan met Stewart twice. Neighbours had called out environmental health because of the state of his garden. The irony is, Swan says, his garden wasn't that bad - the grass slightly overgrown, bits of rubbish scattered, a bush in need of pruning. Stewart didn't let anybody in, so Swan had to catch him when he came home on his bike. Swan asked him to tidy the garden. Stewart agreed. The downstairs window was becoming an eyesore - Swan could see the rubbish mounting up. "Look at the curtains upstairs, they are all dirty. It was like that downstairs. I mentioned it, and he put a lovely white curtain in. He went to a lot of trouble to make sure people didn't see what he was doing. He was a very quiet, private, polite person."

There was little else environmental health could do because there was no obvious problem with smell or rodents. "I haven't been in even now because I can't get in through the door," Swan says. "We didn't have access to the house at all until the police broke in last week." They had been called by neighbours who reported not having seen Stewart for a few days.

Swan and his colleague Jacqui Bromilow talk about how their work has changed since the Human Rights Act became law in 1998. Before that, if individuals were deemed incapable of looking after themselves, the council could intervene. Now, so long as they are not causing a public nuisance, they can live how they like. "We haven't got the right to knock on people's doors and tell them how to live inside their houses," Bromilow says. But that can be frustrating: "So many people, particularly the elderly, are proud and don't want to accept help when they need it."

Swan and Bromilow say hoarding is frighteningly common, and recite any number of cases they've come across. "There was one like this where we didn't find the guy for three and a half months," Swan says. "I'm not particularly squeamish, but the smell was pretty awful. The thing that shocked me, though, was not how bad it was, but that it didn't affect me till I found out more about the guy afterwards. They had to cut his fingers off to fingerprint him. What I found was basically a lump of meat. But what I found at the inquest was a person. The parents turned up, and I discovered that the chap was a professional carpenter, and loved music, and we found his guitar, and after that it was really sad."

Bromilow says there are many triggers. She remembers one hoarder in particular: "There were kettles in the bath, razors in the sink ... Everything was ordered, that's what was unusual. He was in a concentration camp and it's thought he hoarded stuff because in the war everything had a value, whether it be for bargaining with officers or other inmates. So he couldn't throw anything away. Whereas lots of hoarders would just pick up rubbish off the street, here everything was filed."

Next door at number 87, the lawn is perfectly mown and two flowerpots stand to attention at the front door. At number 83, two cars are in the drive, but nobody is answering the door. The few neighbours willing to talk don't want to give their names. Perhaps there is a sense, unspoken, of collective guilt. "He was just Gordon," says an elderly lady. "Tragic. Tragic for all the neighbours, too. We just accepted him. We had no idea what was going on in there. He wasn't a hermit, he was out on his bike all the time."

Some are less sympathetic. A young man passes the house. "Neighbours have been trying to get social services involved for ages but they weren't having any of it. He'd been stinking the place out for years." But social services tell me they were never asked to visit Stewart.

I walk through the town centre in search of clues about Stewart's life. Charity shops seem a good place to start. Nothing. Nobody recognises the description - an elderly man on a bike with a ponytail. But they recognise the symptoms. At the Helen & Douglas House hospice shop, the assistant says she read about Stewart in the local paper, then corrects herself in the next breath. "No, it was a woman. Apparently she felt safe only when she was out shopping, so she bought all this stuff she didn't need. Mountains of stuff. Eventually her shopping fell on her and killed her."

Down the road at the Florence Nightingale hospice shop, manager Joanne Richards says she knows all about hoarders. "One woman in particular. Always ceramics. You could hear her wherever she walked because of her bag - clink, clink, the ceramics. They know they can get things cheap that make them feel happier."

Harj Cheema, owner of the local chippy, apologises for its punning name - TCI [Thank Cod It's] Fried Day. He smiles as soon as I mention Stewart: "He used to come in here every week. Always left his bike outside. He had a nice new one. Always had the same order - cod and two chips. Always by himself." Was he a big man? "No, quite small, frail. He always gave money to the guide dogs." Cheema points to the box in the corner. Was there anything remarkable about him? "No. His hygiene was not too good. I'd have my back to him at the chipper and know it was him because of the smell. He didn't look his age. I'd have thought he was in his 60s. I was shocked to find out how he had died. I read about it - as soon as they said ponytail ..."

Stewart's death has created problems for Parrott & Coales, his solicitors. The circumstances are so mysterious, they have some detective work to do before they can proceed with the will. Tim Friedlander, a partner in the firm, will have to place a statutory public notice in the local paper and wait three months to see if creditors come forward.

He met Stewart 16 years ago, when he made his will. He recalls the bike, the mild eccentricity, that Stewart had been exceptionally close to his mother. He says there is a beneficiary, but cannot provide a name until the will is published. He doubts whether Stewart will have left much of value apart from the house, left to him when his mother died.

A few days later the contractors arrive to empty it. They wear boiler suits and masks, and say they have seen nothing as extreme as this before. The door has been removed, and the sight is even more shocking than we had been led to believe. Supposedly Stewart had burrowed his way in and out through tunnels, but the rubbish is piled solid to the ceiling. Behind one layer of rubbish is another layer, then another - bags of rubbish upon bags of rubbish, TV guides from 10 years ago, a lawnmower, a 4ft electric drill, a couple of mopeds, an unassembled worktop, hundreds of tins of cat food. Every time a bag is carted off, more corroded cat food falls down the stairs. I can't see any tunnels. There doesn't appear to be a way out. It seems Stewart made the decision to barricade himself in and bury himself alive.

I go up to the front door. The whole house looks as if it is about to burst. The rubbish has made it impossible to work out where one room starts and another finishes. Martyn Chuter, environmental health manager for Aylesbury, says the astonishing thing is that there are no flies buzzing around. Neighbours never complained about the smell. "Did he think this was normality, or did he realise there was something strange in the way he lived?" Chuter asks, as if to himself.

Outside, the executor of the will is checking nothing valuable is put into the lorry heading to the landfill. He doesn't want to talk about Stewart. His elderly mother is sitting in the car. She is more talkative. "He loved his cats - he had four or five. I wonder if they're still in there. We knew he stored stuff, it was a bit of a state, but not like this."

None of the neighbours has come out to watch. As people have said, this is a town where privacy is respected. Perhaps a little too much, at times.

In the local pub, the Plough, I make a couple of phone calls to Stewart's neighbours. Terence Dumpleton has lived in the street for 20 years, "The only time I spoke to him was when I was doing Neighbourhood Watching and I asked if he wanted to join. He didn't."

At the bar, Hayley Ball stiffens when I mention Stewart. Yes, she knew him all right. "I helped him when he fell off his bike. It was just after Christmas 2007. I was with my cousin and he got clipped off his bike by a car just in front of us. Not serious, but he hurt his leg, and we just got talking.

"He was going to Tesco's to pick up a prescription and we asked if there was anyone who could do it for him or would he like us to do it, and he just said, 'There is no one, but I'll be all right, I'll do it myself.' He was very independent, quite proud of it, I think. He was all right. He spoke a lot about his life. The fact that he had no family. He talked a bit about how he worked in one of the local firms before they made him redundant. He didn't have another job after that. He just lived on his own. He gave us his address so we could go and see him, but we just didn't get round to it. We saw him about and he'd always say hello and call me Hayley - so he remembered.

"It was shocking really," she says of his death. "I go past his house on the bus and I always think, I hope he's OK. When he gave us his home number he said, call before you come because my house is a bit of a mess. It made me feel guilty when I heard about him because he kind of reached out and I hadn't helped maybe as much as I should." She says even though she didn't really know him, he has left a mark on her. "I've got a two-year-old daughter. It makes you appreciate things like that."

As I leave the pub, the icy wind pinches my face. Maybe Hayley knew Gordon Stewart as well as anybody after chatting to him that day. The thought makes me feel melancholy. I'm beginning to understand what environmental officer Swan said about fleshing out the fact of a death. I have never seen so much as a picture of Gordon, but I'm sure I'd recognise him if we passed in the street.

More stories crop up in the papers about lonely people dying alone, surrounded by their own rubbish. In the same month Stewart dies, we learn about Tony Baxter, 85, from Pinner, who emptied his neighbours' rubbish into his home each week; Joan Cunnane, 77, who was crushed in her Stockport home under 16 years' worth of unopened goods she had bought; and 89-year-old Harold Carr, who hoarded mountains of memorabilia, including a 1937 Bugatti Type 57S Atalante, one of only 17 ever made, which sold for £3.2m at Bonhams' RetroMobile auction in Paris last month. Recently, research carried out by Hammonds Furniture concluded that Britain was a nation of hoarders - the average person accumulates more than a tonne of unwanted stuff, and a quarter of the population said they had been forced to stop using a room because it was so full of stored possessions.

Of course, Gordon Stewart wasn't alone. His hobby/obsession/condition is common enough to have a number of names: compulsive hoarding syndrome, disposophobia, Diogenes syndrome, Collyer brothers syndrome. The disposophobia website states that "disposophobics are generally very smart people who can't, don't or won't make fast value judgments about their 'stuff', so their solution is to keep everything". The Collyer brothers, Homer and Langley, are the most famous disposophobics in history - films have been made about them and books written. They were born in the 1880s, the sons of an eminent Manhattan gynaecologist. After university, they started to hoard and withdrew from the world. The more I find out about them, the more eerie I find the comparisons with Stewart: like him, they collected books and newspapers, and went on from there. Like him, they couldn't, or wouldn't, let anyone in, stacked stuff from floor to ceiling and burrowed their way through tunnels. Like him, they had long hair and are thought to have died of malnutrition.

27 January, the day of Gordon Stewart's funeral. More than 40 people turn up. The Rev Alan Harvey says most didn't know him, though they may well have seen him out and about on his bike. But, he adds, there is a special person here today, Stephen Fennell, a former member of the congregation who will pay tribute to his close friend. The sun is shining through the church windows and the world no longer seems quite as lonely or hopeless as it did a few minutes ago. At the front, a man in his 30s, with a black beard and intense face, is translating the minister's words for his deaf and dumb wife. A few minutes later, he stands at the pew and starts to colour in the blanks of Gordon's life.

"I especially wanted to say something because I believe I was Gordon's closest friend during the last five years or so. To the best of my belief, Gordon Stewart was born on the fifth of May 1934. He never married. He left school at about 13, able to read and write, though not fluently. He lived with his mother till her death in 1975. He was always very attached to her, proud of her, and I am very pleased to think he asked to be buried in her grave at Tring Road cemetery.

"Gordon was a gentle man, highly appreciative of well-made things and art. He owned a number of rare books that cost him tens or even hundreds of pounds, not because he was attracted by their monetary value but because he so admired the workmanship that had gone into them. One book he often told me about was a famous rare book of American birds painted in the 19th century by Audubon. Another was on South American butterflies. He loved animals. My first meeting with him was an illustration of this. I was walking to church, going over the canal bridge. A swan had been chased up from the canal over the pavement by another swan, which was snapping at its tail. The fleeing swan was desperately trying to run across the road to escape and could have easily been hit by a car. I saw Gordon try to block its path with his bicycle. The swan would not give up. In the end someone called the RSPCA. That was the start of my friendship with Gordon.

"He visited me once every two or three weeks, and we would have a meal and chat long into the night. He would tell me the history of Aylesbury as he had witnessed it, the shops that were there in the 30s and 40s, the names of the shopkeepers, who they married, even what school they went to.

"He was unable to invite me to his house because, to his own shame and grief, he'd allowed it to get into a dreadful mess and was too ashamed of it to invite anyone in. Though he could not reciprocate, when we had a meal in my flat he was astonishingly generous and would buy me milk and delicious bread and ham and other groceries.

"Because the newspapers have made so much about the state of his house, I want to say a little in partial defence and explanation, though he knew it had reached an appalling condition and he hated it himself. Before retiring due to ill health, he had to work long hours in the local cash-and-carry store. He would have little time to attend to the house when he got home at night. For some reason he became afraid his neighbours would complain if he put his rubbish out. Before long, the build-up of rubbish inside the house had become so bad that I think he was paralysed at the thought of how to sort it all out. He could not see any way of sorting the good stuff from the bad.

"I'm ever so sad when I think I will never again open my front door and see Gordon." He breaks down, stops, and continues. "Before his death, I did not realise I would feel this as much as I do."

After Fennell's beautiful tribute, we leave the church for Gordon's committal at Tring Road cemetery. Fennell talks with great affection about his old friend. Stewart told him his mother was born into the Hodder publishing family, and he often said he would kill for her. When Gordon was one, his five-year-old brother died. Shortly after, his father passed away. That just left Stewart and his mother. Then, 23 years ago, she died. In later years, he suffered diabetes, and the bike rides up the hill to Sainsbury's, then on to Fennell's home, left him exhausted.

Did Gordon want to die? "He didn't, but he found the state of his life, his home, so horrible, so embarrassing. Like many single men, he was lost. We often talked about tidying up the house, getting a skip. But he was a procrastinator. Me, too."

Fennell throws soil into the grave. He says it was tough for Stewart when he got married a couple of months ago and moved away. Just before Christmas, Fennell and his wife, Virginia, briefly returned to Aylesbury. They planned to visit Gordon, but ran out of time. It was only a few days later that he heard of his death.

What did he like about Gordon? "His simplicity. His friendliness." Did they have much in common? Fennell smiles. "Yes. I used to be messy." He looks at Virginia. "A few years ago I was in a very bad way. My wife is very tidy. I've had to move up several notches to marry Virginia. I often said to Gordon, in years to come I could end up like you."